Feedback control system for applying AC power to ballasted lamps

Abstract

A lighting feedback control system for applying AC power to at least one lamp, which includes a conduction angle controlled phase switching circuit connected in series with the lamp and an AC power source for switching power across the lamp, and a line switching circuit for enabling the application of AC power to the lamp through the phase switching circuit. A light sensor is provided for generating a light control signal indicative of the amount of ambient light present in the predetermined location. Coupled to the light sensing circuit is a phase angle conduction control circuit which generates and applies to a control terminal of the phase switching circuit a phase control signal to control the phase angle conduction time of the phase switching circuit based on the amount of ambient light measured by the light sensing circuit to maintain a constant level of lighting. Integrated within the phase angle conduction control circuit is an RC filter circuit which gradually increases the phase angle conduction time switching circuit from zero, or a predetermined minimum value, to a steady state phase angle conduction time based on the ambient light conditions sensed by the light sensing circuit, after power enabling by the line switching circuit.

What is claimed as new and desired to be secured by Letters Patent of the United States is: 
     
       1. A lighting feedback control system for applying an AC power signal from an AC power source to at least one lamp, comprising: phase switching means connected in series with said lamp and said AC power source for switching power across said lamp, said phase switching means comprising a control terminal for switching said phase switching means to a low impedance state upon application of a phase control signal thereto;   line switching means for enabling the application of AC power to said lamp through said phase switching means;   light sensing means for generating a light control signal indicative of an amount of light present in a predetermined location;   phase angle conduction control means having an input coupled to said light control signal for generating and applying said phase control signal to said control terminal of said phase switching means, said phase angle control means controlling the phase angle conduction time of said phase switching means based on the amount of light measured by said light sensing means to maintain a constant level of lighting, said phase angle control means comprising,   filter means for increasing the phase angle conduction time of said phase switching means from a predetermined minimum value to a steady state phase angle conduction time based on said light control signal after power enabling by said line switching means;   wherein said phase angle conduction control means comprises output disabling means coupled to said light sensing means for disabling the switching of said phase switching means when said light control signal has a first level indicative of a first predetermined amount of light, comprising   hysteresis circuit means for maintaining disabled the switching of said phase switching means after said light control signal has said first level until said light control signal has a second level indicative of a second predetermined amount of light.   
     
     
       2. A lighting feedback control system according to claim 1, wherein said phase angle control means further comprises: sweep generating means for generating a ramp signal at twice the frequency and in synchronization with said AC power signal,   said filter means comprising a low pass filter having an input coupled to said light control signal and producing a filtered light control signal at an output thereof,   first comparator means having said ramp signal and said filtered light control signal as inputs for producing a gating pulse signal each time the level of said ramp signal drops below the level of said filtered first control signal, said gating pulse signal applied to the phase control terminal of said phase switching means.   
     
     
       3. A system according to claim 1 wherein said line switching means comprises: a line switch connected in series between said AC source and one side of said lamp, said phase switching means connected in series between the other side of said lamp and said AC power source.   
     
     
       4. A system according to claim 2, wherein said phase control means further comprises: level clamping means coupled to said filter means for clamping the filtered light control signal to said first comparator means between first and second control levels.   
     
     
       5. A system according to claim 4, wherein said level clamping means comprises: first and second operational amplifiers each having an inverting input connected to said filtered light control signal,   first level setting means coupled to a non-inverting input of said first operational amplifier for setting a maximum level for said filtered light control signal,   second level setting means coupled to a non-inverting input of said second operational amplifier for setting a minimum level for said filtered light control signal;   a first diode having an anode connected to the output of said first operational amplifier and a cathode coupled to said filtered light control signal, and   a second diode having a cathode connected to the output of said second operational amplifier and an anode coupled to said filtered light control signal.   
     
     
       6. A system according to claim 1, wherein said phase switching means comprises: a triac.   
     
     
       7. A lighting feedback control system for applying an AC power signal from an AC power source to at least one lamp, comprising: phase switching means connected in series with said lamp and said AC power source for switching power across said lamp, said phase switching means comprising a control terminal for switching said phase switching means to a low impedance state upon application of a phase control signal thereto;   line switching means for enabling the application of AC power to said lamp through said phase switching means;   light sensing means for generating a light control signal indicative of an amount of light present in a predetermined location;   phase angle conduction control means having an input coupled to said light control signal for generating and applying said phase control signal to said control terminal of said phase switching means, said phase angle control means controlling the phase angle conduction time of said phase switching means based on the amount of light measured by said light sensing means to maintain a constant level of lighting, said phase angle control means comprising,   filter means for increasing the phase angle conduction time of said phase switching means from a predetermined minimum value to a steady state phase angle conduction time based on said light control signal after power enabling by said line switching means;   wherein said phase angle control means further comprises:   sweep generating means for generating a ramp signal at twice the frequency and in synchronization with said AC power signal,   said filter means comprising a low pass filter having an input coupled to said light control signal and producing a filtered light control signal at an output thereof,   first comparator means having said ramp signal and said filtered light control signal as inputs for producing a gating pulse signal each time the level of said ramp signal drops below the level of said filtered first control signal, said gating pulse signal applied to the phase control terminal of said phase switching means,   level clamping means coupled to said filter means for clamping the filtered light control signal to said first comparator means between first and second control levels, including   first and second operational amplifiers each having an inverting input connected to said filtered light control signal,   first level setting means coupled to a non-inverting input of said first operational amplifier for setting a maximum level for said filtered light control signal,   second level setting means coupled to a non-inverting input of said second operational amplifier for setting a minimum level for said filtered light control signal;   a first diode having an anode connected to the output of said first operational amplifier and a cathode coupled to said filtered light control signal, and   a second diode having a cathode connected to the output of said second operational amplifier and an anode coupled to said filtered light control signal.